Hybrid vehicle

ABSTRACT

When the required driving force is larger than the first upper limit driving force, the control device sets a target compensation power of a power storage device, based on a difference between the required driving force and the first upper limit driving force. Further, the control device gradually increases a working compensation power toward the target compensation power when the gear ratio of the stepped transmission is changed, compared with an increase in the working compensation power when the gear ratio of the stepped transmission is not changed.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present disclosure claims priority to Japanese Patent ApplicationNo. 2019-157046 filed Aug. 29, 2019, which is incorporated herein byreference in its entirety including specification, drawings and claims.

TECHNICAL FIELD

The present disclosure relates to a hybrid vehicle.

BACKGROUND

In a proposed configuration of a hybrid vehicle, a planetary gear has asun gear connected with a first motor, a carrier connected with anengine, a ring gear connected with a transmission member, thetransmission member connected with a second motor, a steppedtransmission placed between the transmission member and a driveshaftlinked with an axle, and a battery connected with the first motor andwith the second motor via power lines (as described in, for example, JP2017-159732A). This hybrid vehicle sets a required driving force that isrequired for the driveshaft, based on an accelerator position and avehicle speed. This hybrid vehicle also sets a gear ratio to the gearratio of the stepped transmission by taking into account a virtual gearratio based on the accelerator position and the vehicle speed. Thishybrid vehicle sets a drivability rotation speed of the engine, based onthe vehicle speed and the gear ratio. This hybrid vehicle sets an upperlimit power of the engine when the engine is operated at the drivabilityrotation speed. This hybrid vehicle sets an upper limit driving force ofthe driveshaft when the upper limit power is output from the engine.This hybrid vehicle controls the engine, the first motor, the secondmotor, and the stepped transmission such that the engine is operated atthe drivability rotation speed and the smaller between the requireddriving force and the upper limit driving force is output to thedriveshaft. In this hybrid vehicle, such control causes the rotationspeed of the engine to be a rotation speed according to the vehiclespeed even when the driver steps on an accelerator pedal. This hybridvehicle gives the driver the better drive feeling, compared with aconfiguration abruptly increases the rotation speed of the engine priorto an increase in the vehicle speed. In this hybrid vehicle, therotation speed of the engine varies with a change in the gear ratio.This hybrid vehicle accordingly gives the driver the feeling of speedchange.

SUMMARY

In the hybrid vehicle described above, it is possible to increase atorque output from the second motor to the drive shaft by using electricpower of the battery in order to output larger driving force than theupper limit driving force to the drive shaft when the required drivingforce becomes larger than the upper limit driving force. When thiscontrol overlaps with the change of the gear ratio of the steppedtransmission, a variation of the driving force output to the drive shaftbecomes larger depending on how such control is performed. This maycause a gear shift shock.

A main object of a hybrid vehicle of the present disclosure is tosuppress a gear shift shock.

In order to achieve the above main object, the hybrid vehicle of thepresent disclosure employs the following configuration.

The present disclosure is directed to a hybrid vehicle. The hybridvehicle includes an engine, a first motor, a planetary gear includingthree rotational elements that are respectively connected with theengine, the first motor and a transmission member, a steppedtransmission placed between the transmission member and a driveshaftlinked with an axle, a second motor configured to input and output powerfrom and to the transmission member or the driveshaft, a power storagedevice configured to transmit electric power to and from the first motorand the second motor, and a control device. The control device isprogrammed to set a required driving force that is required for thedriveshaft, based on an operation amount of an accelerator and a vehiclespeed, set a simulated gear ratio from a gear ratio of the steppedtransmission or from the gear ratio of the stepped transmission bytaking into account a virtual gear ratio and set a target gear ratio ofthe stepped transmission, based on the operation amount of theaccelerator and the vehicle speed or based on a driver's shiftoperation, set a target rotation speed of the engine, based on thevehicle speed and the simulated gear ratio, set an upper limit power ofthe engine when the engine is operated at the target rotation speed, seta first upper limit driving force of the driveshaft when the upper limitpower is output from the engine, set a target driving force of thedriveshaft according to a magnitude relationship between the requireddriving force and the first upper limit driving force, and control theengine, the first motor, the second motor and the stepped transmission,such that the engine is operated at the target rotation speed, the gearratio of the stepped transmission becomes equal to the target gearratio, and the hybrid vehicle is driven based on the target drivingforce. When the required driving force is equal to or smaller than thefirst upper limit driving force, the control device is programmed to setthe target driving force to the required driving force, and when therequired driving force is larger than the first upper limit drivingforce, the control device is programmed to set a target compensationpower of the power storage device, based on a difference between therequired driving force and the first upper limit driving force. Thecontrol device is programmed to set a second upper limit driving forceof the driveshaft when the upper limit power is output from the engineand the power storage device is charged or discharged according to aworking compensation power based on the target compensation power, andthe control device sets the target driving force to the smaller betweenthe required driving force and the second upper limit driving force. Thecontrol device is programmed to gradually increase the workingcompensation power toward the target compensation power when the gearratio of the stepped transmission is changed, compared with an increasein the working compensation power when the gear ratio of the steppedtransmission is not changed.

In the hybrid vehicle according to this aspect of the presentdisclosure, when the required driving force is equal to or smaller thanthe first upper limit driving force, the control device sets the targetdriving force to the required driving force. When the required drivingforce is larger than the first upper limit driving force, the controldevice sets the target compensation power of the power storage device,based on the difference between the required driving force and the firstupper limit driving force. The control device sets the second upperlimit driving force of the driveshaft when the upper limit power isoutput from the engine and the power storage device is charged ordischarged with the power based on the target compensation power. Thecontrol device sets the target driving force to the smaller between therequired driving force and the second upper limit driving force.Further, the control device gradually increases the working compensationpower toward the target compensation power when the gear ratio of thestepped transmission is changed, compared with the increase in theworking compensation power when the gear ratio of the steppedtransmission is not changed. The hybrid vehicle of the presentdisclosure further suppresses the variation of the driving force outputto the drive shaft with the change of the gear ratio of the steppedtransmission, and suppresses the gear shift shock.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a configuration diagram illustrating the schematicconfiguration of a hybrid vehicle according to one embodiment of thepresent disclosure;

FIG. 2 is a configuration diagram illustrating the schematicconfiguration of an engine, a planetary gear, motors MG1 and MG2 and astepped transmission;

FIG. 3 is an operation table showing a relationship between therespective speeds of the stepped transmission and the states of clutchesC1 and C2 and brakes B1, B2 and B3;

FIG. 4 is alignment charts showing a relationship among the rotationspeeds of respective rotational elements of the planetary gear and arelationship among the rotation speeds of respective rotational elementsof the stepped transmission;

FIG. 5 is a flowchart showing one example of a drivability prioritycontrol routine (first half);

FIG. 6 is a flowchart showing one example of the drivability prioritycontrol routine (latter half);

FIG. 7 is a diagram illustrating one example of a required driving forcesetting map;

FIG. 8 is a diagram illustrating one example of a gear shift line chart;

FIG. 9 is a diagram illustrating one example of a drivability rotationspeed setting map;

FIG. 10 is a diagram illustrating one example of an upper limit powersetting map;

FIG. 11 is a diagram illustrating one example of a required chargedischarge power setting map;

FIG. 12 is a diagram illustrating one example of a compensable powersetting map;

FIG. 13 is a diagram illustrating one example of variations in anaccelerator position Acc, a vehicle speed V, a simulated gear ratio Gsv,a target gear ratio Gsat*, a target rotation speed Ne* and an actualrotation speed Ne of the engine, a target power Pe* and an actual outputpower Pe of the engine, a required driving force Tdusr, an upper limitdriving force Tdlim1, a required charge discharge power Pb1* and Pb2*and an actual charge discharge power Pb of the battery, a target drivingforce Td*, and an output driving force Td when the gear ratio Gsat ofthe stepped transmission is not changed;

FIG. 14 is a diagram illustrating one example of variations in theaccelerator position Acc, the vehicle speed V, the simulated gear ratioGsv, the target gear ratio Gsat*, the required driving force Tdusr, therequired charge discharge power Pb2* of the battery, and a torquecommand Tm2* of the motor MG2 when the gear ratio Gsat of the steppedtransmission is upshifted;

FIG. 15 is a flowchart showing one example of the drivability prioritycontrol routine (latter half) according to a modification;

FIG. 16 is a diagram illustrating one example of variations in theaccelerator position Acc, the vehicle speed V, the simulated gear ratioGsv, the target gear ratio Gsat*, the required driving force Tdusr, therequired charge discharge power Pb2* of the battery, and the torquecommand Tm2* of the motor MG2 when the accelerator position Acc becomeslarger than a reference value Aref during a battery power compensation;

FIG. 17 is a flowchart showing one example of the drivability prioritycontrol routine (latter half) according to another modification;

FIG. 18 is a diagram illustrating one example of variations in theaccelerator position Acc, the vehicle speed V, the simulated gear ratioGsv, the target gear ratio Gsat*, the required driving force Tdusr, therequired charge discharge power Pb2* of the battery, and the torquecommand Tm2* of the motor MG2 when the accelerator position Acc becomeslarger than the reference value Aref during a battery powercompensation, and subsequently, the charge discharge power Pb* of thebattery has a positive value and the gear ratio Gsat of the steppedtransmission is changed;

FIG. 19 is a flowchart showing one example of the drivability prioritycontrol routine (latter half) according to another modification; and

FIG. 20 is a flowchart showing one example of the drivability prioritycontrol routine (first half) according to another modification.

DESCRIPTION OF EMBODIMENTS

The following describes some aspects of the disclosure with reference toembodiments.

FIG. 1 is a configuration diagram illustrating the schematicconfiguration of a hybrid vehicle 20 according to one embodiment of thepresent disclosure. FIG. 2 is a configuration diagram illustrating theschematic configuration of an engine 22, a planetary gear 30, motors MG1and MG2 and a stepped transmission 60. As illustrated in FIGS. 1 and 2,the hybrid vehicle 20 of the embodiment includes an engine 22, aplanetary gear 30, motors MG1 and MG2, inverters 41 and 42, a battery 50serving as a power storage device, a stepped transmission 60, and ahybrid electronic control unit (hereinafter referred to as “HVECU”) 70.

The engine 22 is configured as an internal combustion engine to outputpower by using, for example, gasoline or light oil as a fuel. Thisengine 22 is operated and controlled by an engine electronic controlunit (hereinafter referred to as “engine ECU”) 24.

The engine ECU 24 includes a microcomputer including a CPU, a ROM, aRAM, input/output ports, and a communication port. Signals from varioussensors required for operating and controlling the engine 22 are inputinto the engine ECU 24 via the input port. The signals input into theengine ECU 24 include, for example, a crank angle θcr of a crankshaft 23from a crank position sensor 23 a configured to detect the rotationalposition of the crankshaft 23 of the engine 22. The engine ECU outputsvarious control signals for operating and controlling the engine 22 viathe output port. The engine ECU 24 is connected with the HVECU 70 viarespective communication ports. The engine ECU 24 calculates a rotationspeed Ne of the engine 22, based on the crank angle θcr input from thecrank position sensor 23 a.

The planetary gear 30 is configured as a single pinion-type planetarygear mechanism. This planetary gear 30 includes a sun gear 30 s as anexternal gear, a ring gear 30 r as an internal gear, a plurality ofpinion gears 30 p respectively engaged with the sun gear 30 s and thering gear 30 r, and a carrier 30 c provided to support the plurality ofpinion gears 30 p to be rotatable on their axes and revolvable. The sungear 30 s is connected with a rotor of the motor MG1. The ring gear 30 ris connected with a rotor of the motor MG2 and with an input shaft 61 ofthe stepped transmission 60 via a transmission member 32. The carrier 30c is connected with the crankshaft 23 of the engine 22 via a damper 28.

Both the motors MG1 and MG2 are configured, for example, as synchronousgenerator motors. The rotor of the motor MG1 is connected with the sungear 30 s of the planetary gear 30 as described above. The rotor of themotor MG2 is connected with the ring gear 30 r of the planetary gear 30and with the input shaft 61 of the stepped transmission 60 via thetransmission member 32 as described above. The inverters 41 and 42 areused to drive the motors MG1 and MG2 and are connected with the battery50 via power lines 54. A motor electronic control unit (hereinafterreferred to as “motor ECU”) 40 performs switching control of a pluralityof switching elements (not shown) included in the inverters 41 and 42,so as to rotate and drive the motors MG1 and MG2.

The motor ECU 40 includes a microcomputer including a CPU, a ROM, a RAM,input/output ports, and a communication port. Signals from varioussensors required for driving and controlling the motors MG1 and MG2 areinput into the motor ECU 40 via the input port. The signals input intothe motor ECU 40 include, for example, rotational positions θm1 and θm2of the respective rotors of the motor MG1 and MG2 from rotationalposition sensors 43 and 44 configured to detect the rotational positionsof the respective rotors of the motors MG1 and MG2 and phase currentsIu1, Iv1, Iu2 and Iv2 of respective phases of the motors MG1 and MG2from current sensors configured to detect the phase currents flowing inthe respective phases of the motors MG1 and MG2. The motor ECU 40outputs, for example, switching control signals to the plurality ofswitching elements (not shown) included in the inverters 41 and 42 viathe output port. The motor ECU 40 is connected with the HVECU 70 via therespective communication ports. The motor ECU 40 calculates electricalangles θe1 and θe2 and rotation speeds Nm1 and Nm2 of the motors MG1 andMG2, based on the rotational positions θm1 and θm2 of the respectiverotors of the motor MG1 and MG2 input from the rotational positionsensors 43 and 44.

The battery 50 is configured as, for example, a lithium ion rechargeablebattery or a nickel metal hydride battery. This battery 50 is connectedwith the inverters 41 and 42 via the power lines 54 as described above.The battery 50 is under management of a battery electronic control unit(hereinafter referred to as “battery ECU”) 52.

The battery ECU 52 includes a microcomputer including a CPU, a ROM, aRAM, input/output ports, and a communication port. Signals from varioussensors required for management of the battery 50 are input into thebattery ECU 52 via the input port. The signals input into the batteryECU 52 include, for example, a voltage Vb of the battery 50 from avoltage sensor 51 a placed between terminals of the battery 50, anelectric current Ib of the battery 50 from a current sensor 51 b mountedto an output terminal of the battery 50, and a temperature Tb of thebattery 50 from a temperature sensor 51 c mounted to the battery 50. Thebattery ECU 52 is connected with the HVECU 70 via the respectivecommunication ports. The battery ECU 52 calculates a state of charge SOCof the battery 50, based on an integrated value of the electric currentIb of the battery 50 input from the current sensor 51 b. The state ofcharge SOC denotes a ratio of the capacity of electric powerdischargeable from the battery 50 to the total capacity of the battery50. The battery ECU 52 also calculates an input limit Win and an outputlimit Wout of the battery 50, based on the state of charge SOC of thebattery 50 and the temperature Tb of the battery 50 input from thetemperature sensor 51 c. The input limit Win denotes a maximum allowablepower (negative value) to charge the battery 50. The output limit Woutdenotes a maximum allowable power (positive value) to be discharged fromthe battery 50.

The stepped transmission 60 is configured as a four-speed steppedtransmission. This stepped transmission 60 includes the input shaft 61,an output shaft 62, planetary gears 63, 64 and 65, clutches C1 and C2,and brakes B1, B2 and B3. The input shaft 61 is connected with the ringgear 30 r of the planetary gear 30 and with the motor MG2 via thetransmission member 32 as described above. The output shaft 62 isconnected with a driveshaft 36 that is linked with drive wheels 39 a and39 b via a differential gear 38.

The planetary gear 63 is configured as a single pinion-type planetarygear mechanism. This planetary gear 63 includes a sun gear 63 s as anexternal gear, a ring gear 63 r as an internal gear, a plurality ofpinion gears 63 p respectively engaged with the sun gear 63 s and thering gear 63 r, and a carrier 63 c provided to support the plurality ofpinion gears 63 p to be rotatable on their axes and revolvable.

The planetary gear 64 is configured as a single pinion-type planetarygear mechanism. This planetary gear 64 includes a sun gear 64 s as anexternal gear, a ring gear 64 r as an internal gear, a plurality ofpinion gears 64 p respectively engaged with the sun gear 64 s and thering gear 64 r, and a carrier 64 c provided to support the plurality ofpinion gears 64 p to be rotatable on their axes and revolvable.

The planetary gear 65 is configured as a single pinion-type planetarygear mechanism. This planetary gear 65 includes a sun gear 65 s as anexternal gear, a ring gear 65 r as an internal gear, a plurality ofpinion gears 65 p respectively engaged with the sun gear 65 s and thering gear 65 r, and a carrier 65 c provided to support the plurality ofpinion gears 65 p to be rotatable on their axes and revolvable.

The sun gear 63 s of the planetary gear 63 and the sun gear 64 s of theplanetary gear 64 are linked with (fixed to) each other. The ring gear63 r of the planetary gear 63, the carrier 64 c of the planetary gear 64and the carrier 65 c of the planetary gear 65 are linked with oneanother. The ring gear 64 r of the planetary gear 64 and the sun gear 65s of the planetary gear 65 are linked with each other. Accordingly, theplanetary gears 63, 64 and 65 serve as five element-type mechanism usingthe sun gear 63 s of the planetary gear 63 with the sun gear 64 s of theplanetary gear 64; the carrier 63 c of the planetary gear 63; the ringgear 65 r of the planetary gear 65; the ring gear 63 r of the planetarygear 63 with the carrier 64 c of the planetary gear 64 and the carrier65 c of the planetary gear 65; and the ring gear 64 r of the planetarygear 64 with the sun gear 65 s of the planetary gear 65, as fiverotational elements. The ring gear 63 r of the planetary gear 63, thecarrier 64 c of the planetary gear 64 and the carrier 65 c of theplanetary gear 65 are linked with the output shaft 62.

The clutch C1 is configured to connect and disconnect the input shaft 61with and from the ring gear 64 r of the planetary gear 64 and the sungear 65 s of the planetary gear 65. The clutch C2 is configured toconnect and disconnect the input shaft 61 with and from the sun gear 63s of the planetary gear 63 and the sun gear 64 s of the planetary gear64.

The brake B1 is configured to fix (connect) the sun gear 63 s of theplanetary gear 63 and the sun gear 64 s of the planetary gear 64 to(with) a transmission case 69 such as to be not rotatable and to releasethe sun gear 63 s and the sun gear 64 s from the transmission case 69such as to be rotatable. The brake B2 is configured to fix (connect) thecarrier 63 c of the planetary gear 63 to and from the transmission case69 such as to be not rotatable and to release the carrier 63 c from thetransmission case 69 such as to be rotatable. The brake B3 is configuredto fix (connect) the ring gear 65 r of the planetary gear 65 to (with)the transmission case 69 such as to be not rotatable and to release thering gear 65 r from the transmission case 69 such as to be rotatable.

The clutches C1 and C2 are respectively configured as, for example,hydraulically actuated multiple disc clutches. The brake B1 isconfigured as, for example, a hydraulically actuated band brake. Thebrakes B2 and B3 are respectively configured as, for example,hydraulically actuated multiple disc brakes. The clutches C1 and C2 andthe brakes B1, B2 and B3 are operated through supply and discharge ofhydraulic oil by a hydraulic controller (not shown). The hydrauliccontroller is controlled by the HVECU 70.

FIG. 3 is an operation table showing a relationship between therespective speeds of the stepped transmission 60 and the states of theclutches C1 and C2 and the brakes B1, B2 and B3. FIG. 4 is alignmentcharts showing a relationship among the rotation speeds of therespective rotational elements of the planetary gear 30 and arelationship among the rotation speeds of the respective rotationalelements of the stepped transmission 60. In the charts of FIG. 4, “ρ0”denotes a gear ratio of the planetary gear 30 (the number of teeth ofthe sun gear 30 s/the number of teeth of the ring gear 30 r), “ρ1”denotes a gear ratio of the planetary gear 63 (the number of teeth ofthe sun gear 63 s/the number of teeth of the ring gear 63 r), “ρ2”denotes a gear ratio of the planetary gear 64 (the number of teeth ofthe sun gear 64 s/the number of teeth of the ring gear 64 r), and “ρ3”denotes a gear ratio of the planetary gear 65 (the number of teeth ofthe sun gear 65 s/the number of teeth of the ring gear 65 r).

In FIG. 4, the left side is the alignment chart of the planetary gear30, and the right side is the alignment chart of the steppedtransmission 60. In the alignment chart of the planetary gear 30, a 30 saxis indicates a rotation speed of the sun gear 30 s that is equal to arotation speed Nm1 of the motor MG1. A 30 c axis indicates a rotationspeed of the carrier 30 c that is equal to a rotation speed Ne of theengine 22. A 30 r axis indicates a rotation speed of the ring gear 30 rthat is equal to a rotation speed Nm2 of the motor MG2, a rotation speedof the transmission member 32, and a rotation speed of the input shaft61. In the alignment chart of the stepped transmission 60, a 63 s-64 saxis indicates rotation speeds of the sun gear 63 s of the planetarygear 63 and of the sun gear 64 s of the planetary gear 64. A 63 c axisindicates a rotation speed of the carrier 63 c of the planetary gear 63.A 65 r axis indicates a rotation speed of the ring gear 65 r of theplanetary gear 65. A 63 r-64 c-65 c axis indicates rotation speeds ofthe ring gear 63 r of the planetary gear 63, of the carrier 64 c of theplanetary gear 64 and of the carrier 65 c of the planetary gear 65 thatare equal to a rotation speed Nd of the driveshaft 36 (i.e., a rotationspeed of the output shaft 62). A 64 r-65 s axis indicates rotationspeeds of the ring gear 64 r of the planetary gear 64 and of the sungear 65 s of the planetary gear 65.

In the stepped transmission 60, the clutches C1 and C2 and the brakesB1, B2 and B3 are engaged and disengaged to provide forward gear ratiosof a first speed to a fourth speed and a reverse gear ratio as shown inFIG. 3. More specifically, the forward gear ratio of the first speed isprovided by engaging the clutch C1 and the brake B3 and disengaging theclutch C2 and the brakes B1 and B2. The forward gear ratio of the secondspeed is provided by engaging the clutch C1 and the brake B2 anddisengaging the clutch C2 and the brakes B1 and B3. The forward gearratio of the third speed is provided by engaging the clutch C1 and thebrake B1 and disengaging the clutch C2 and the brakes B2 and B3. Theforward gear ratio of the fourth speed is provided by engaging theclutches C1 and C2 and disengaging the brakes B1, B2 and B3. The reversegear ratio is provided by engaging the clutch C2 and the brake B3 anddisengaging the clutch C1 and the brakes B1 and B2.

The HVECU 70 includes a microcomputer including a CPU, a ROM, a RAM,input/output ports, and a communication port. Signals from varioussensors are input into the HVECU 70 via the input port. The signalsinput into the HVECU 70 include, for example, a rotation speed Nd of thedriveshaft 36 from a rotation speed sensor 36 a configured to detect therotation speed of the driveshaft 36, an ignition signal from an ignitionswitch 80 and a shift position SP from a shift position sensor 82configured to detect an operating position of a shift lever 81. Thesignals input into the HVECU 70 also include an accelerator position Accfrom an accelerator pedal position sensor 84 configured to detect adepression amount of an accelerator pedal 83 and a brake pedal positionBP from a brake pedal position sensor 86 configured to detect adepression amount of a brake pedal 85. The signals input into the HVECU70 further include a vehicle speed V from a vehicle speed sensor 88, aroad surface gradient Ord from a gradient sensor 89 (which has apositive value in the case of an uphill road), and a mode signal from amode switch 90. The HVECU 70 outputs various control signals via theoutput port. The signals output from the HVECU 70 include, for example,a control signal to the stepped transmission 60 (hydraulic controller).The HVECU 70 is connected with the engine ECU 24, the motor ECU 40 andthe battery ECU 52 via the respective communication ports as describedabove.

The shift position SP herein includes a parking position (P position), areverse position (R position), a neutral position (N position) and adrive position (D position).

The mode switch 90 serves as a switch operated by the driver to select aworking drive mode out of a plurality of drive modes including anordinary mode that gives priority to the fuel consumption and adrivability priority mode that gives priority to the driver's drivefeeling (drivability) over the fuel consumption. When the ordinary modeis selected as the working drive mode, the engine 22 and the motors MG1and MG2 are driven and controlled, such that the hybrid vehicle 20 isdriven with efficiently operating the engine 22 at the shift position SPset to the D position. When the drivability priority mode is selected asthe working drive mode, on the other hand, the engine 22 and the motorsMG1 and MG2 are driven and controlled, such that the hybrid vehicle 20is driven with operating the engine 22 as if the engine 22 is connectedwith the driveshaft 36 via a virtual 10-speed stepped transmission(hereinafter referred to as “simulated transmission”) at the shiftposition SP set to the D position. The respective gear ratios of theten-speed simulated transmission are configured such that two virtualgear ratios are provided with regard to each of the gear ratios of thefirst to the third speeds of the four-speed stepped transmission 60.

The hybrid vehicle 20 of the embodiment including the configurationdescribed above is driven by hybrid drive (HV drive) with operation ofthe engine 22 or by electric drive (EV drive) without operation of theengine 22.

The following describes the operations of the hybrid vehicle 20configured as described above or more specifically a series ofoperations when the hybrid vehicle 20 is driven by HV drive at the shiftposition SP set to the D position with selection of the drivabilitypriority mode as the working drive mode by the driver's operation of themode switch 90. FIG. 5 and FIG. 6 are flowcharts showing one example ofa drivability priority control routine performed by the HVECU 70. Thisroutine is performed repeatedly when the hybrid vehicle 20 is driven byHV drive at the shift position SP set to the D position with selectionof the drivability priority mode as the working drive mode by thedriver's operation of the mode switch 90.

When the drivability priority control routine of FIGS. 5 and 6 istriggered, the HVECU 70 first obtains input data of, for example, theaccelerator position Acc, the vehicle speed V, the rotation speed Nd ofthe driveshaft 36, the rotation speed Ne of the engine 22, the rotationspeeds Nm1 and Nm2 of the motors MG1 and MG2 and the state of charge SOCand the output limit Wout of the battery 50 (step S100). The acceleratorposition Acc input here is a value detected by the accelerator pedalposition sensor 84. The vehicle speed V input here is a value detectedby the vehicle speed sensor 88. The rotation speed Nd of the driveshaft36 input here is a value detected by the rotation speed sensor 36 a. Therotation speed Ne of the engine 22 input here is a value calculated bythe engine ECU 24. The rotation speeds Nm1 and Nm2 of the motors MG1 andMG2 input here are values calculated by the motor ECU 40. The state ofcharge SOC and the output limit Wout of the battery 50 input here arevalues calculated by the battery ECU 52.

The HVECU 70 sets a required driving force Tdusr that is required fordriving (required for the driveshaft 36) according to a required drivingforce setting map by using the accelerator position Acc and the vehiclespeed V (step S110). The required driving force setting map is set inadvance to specify a relationship among the accelerator position Acc,the vehicle speed V and the required driving force Tdusr and is storedin the non-illustrated ROM. FIG. 7 is a diagram illustrating one exampleof the required driving force setting map.

The HVECU 70 subsequently sets a simulated gear ratio Gsv and a targetgear ratio Gsat* according to a gear shift line chart by using theaccelerator position Acc and the vehicle speed V (step S120). Thesimulated gear ratio Gsv denotes a gear ratio of the ten-speed simulatedtransmission. The target gear ratio Gsat* denotes a target gear ratio ofthe four-speed stepped transmission 60. The gear shift line chart is setin advance to specify a relationship among the accelerator position Acc,the vehicle speed V, the simulated gear ratio Gsv and the target gearratio Gsat*.

FIG. 8 is a diagram illustrating one example of the gearshift linechart. In the diagram, solid lines (thin solid lines and thick solidlines) indicate gear shift lines for upshift, and broken lines (thinbroken lines and thick broken lines) indicate gear shift lines fordownshift. The simulated gear ratio Gsv is set as one of the respectivegear ratios of the ten speeds to be corresponded to, based on all thegear shift lines shown in FIG. 8. The target gear ratio Gsat* is set asone of the respective gear ratios of the four speeds to be correspondedto, based on the gear shift lines of the thick solid lines and the thickbroken lines shown in FIG. 8.

After setting the target gear ratio Gsat*, the HVECU 70 controls thestepped transmission 60 by using the target gear ratio Gsat* (stepS130). When a gear ratio Gsat is equal to the target gear ratio Gsat*,the stepped transmission 60 keeps the gear ratio Gsat unchanged. Whenthe gear ratio Gsat is different from the target gear ratio Gsat*, onthe other hand, the stepped transmission 60 changes the gear ratio Gsat,such that the gear ratio Gsat becomes equal to the target gear ratioGsat*. The stepped transmission 60 is similarly controlled when thehybrid vehicle 20 is driven by HV drive or by EV drive with selection ofthe ordinary mode as the working drive mode. The process of changing thegear ratio Gsat takes the longer time than the execution cycle of thisroutine.

The gear ratio Gsat is changed, for example, in the following manner.The HVECU 70 first performs a first stage release control with regard toa release side element that switches from engaged state to disengagedstate accompanied with the change of the gear ratio Gsat among theclutches C1 and C2 and the brakes B1, B2, and B3 of the steppedtransmission 60. Further, the HVECU 70 performs a stroke control withregard to an engagement side element that switches from the disengagedstate to the engaged state among the clutches C1 and C2 and the brakesB1, B2, and B3 of the stepped transmission 60. The first stage releasecontrol is a control in which a hydraulic pressure is reduced by onestage and the release side element is slip-engaged. The stroke controlis a control that performs a fast fill that fills a gap between a pistonof the engagement side element and a friction engagement plate (strokethe piston), and subsequently performs a low-pressure standby that holdsthe hydraulic pressure at a relatively low standby pressure.

The HVECU 70 subsequently performs a second stage release control withregard to the release side element, and performs a torque phase controlwith regard to the engagement side element. The second stage releasecontrol and the torque phase control are controls that gradually reducethe hydraulic pressure of the release side element, gradually increasethe hydraulic pressure of the engagement side element, and change atorque transmission from a torque transmission by a gear ratio beforethe change to a torque transmission by the gear ratio after the change.

The HVECU 70 subsequently performs a third stage release control withregard to the release side element, and performs an inertia phasecontrol and a terminal control in this order with regard to theengagement side element. The third stage release control is a controlthat further reduces the hydraulic pressure of the release side element.The inertia phase control is a control that further gradually increasesthe hydraulic pressure of the engagement side element to bring therotation speed Nin of the input shaft 61 of the stepped transmission 60close to the rotation speed corresponding to the target gear ratioGsat*. The terminal control is a control that further increases thehydraulic pressure of the engagement side element.

After setting the simulated gear ratio Gsv at step S120, the HVECU 70sets a drivability rotation speed Nedrv of the engine 22 according to adrivability rotation speed setting map by using the vehicle speed V andthe simulated gear ratio Gsv (step S140). The HVECU 70 subsequently setsa target rotation speed Ne* of the engine 22 to the drivability rotationspeed Nedrv of the engine 22 (step S150). The drivability rotation speedsetting map is set in advance to specify a relationship among thevehicle speed V, the simulated gear ratio Gsv and the drivabilityrotation speed Nedrv of the engine 22 and is stored in thenon-illustrated ROM.

FIG. 9 is a diagram illustrating one example of the drivability rotationspeed setting map. As illustrated, the drivability rotation speed Nedrvof the engine 22 is set to linearly increase with an increase in thevehicle speed V at each of the simulated gear ratios Gsv of theten-speed simulated transmission and to provide the smaller slopeagainst the vehicle speed V at the larger simulated gear ratio Gsv ofthis simulated transmission. When the engine 22 is operated at thedrivability rotation speed Nedrv, such setting causes the rotation speedNe of the engine 22 to increase with an increase in the vehicle speed Vat each of the simulated gear ratios Gsv of the ten-speed simulatedtransmission. The rotation speed Ne of the engine 22 decreases in thecourse of upshift of the simulated gear ratio Gsv and increases in thecourse of downshift of the simulated gear ratio Gsv. As a result, thehybrid vehicle 20 causes the behavior of the rotation speed Ne of theengine 22 to become closer to the behavior of an engine rotation speedof a motor vehicle equipped with an actual ten-speed steppedtransmission.

After setting the target rotation speed Ne* of the engine 22, the HVECU70 sets an upper limit power Pelim of the engine 22 according to anupper limit power setting map by using the target rotation speed Ne* ofthe engine 22 (step S160). The upper limit power Pelim of the engine 22denotes an upper limit of power that can be output from the engine 22when the engine 22 is operated at the target rotation speed Ne*(drivability rotation speed Nedrv). The upper limit power setting map isset in advance to specify a relationship between the target rotationspeed Ne* and the upper limit power Pelim of the engine 22 and is storedin the non-illustrated ROM. FIG. 10 is a diagram illustrating oneexample of the upper limit power setting map. As illustrated, the upperlimit power Pelim of the engine 22 is set to increase with an increasein the target rotation speed Ne* of the engine 22.

The HVECU 70 subsequently sets a required charge discharge power Pb1* ofthe battery 50 (which has a positive value when the battery 50 isdischarged) such that the state of charge SOC of the battery 50 becomescloser to a target state of charge SOC*, according to a required chargedischarge power setting map by using the state of charge SOC of thebattery 50 (step S170). The required charge discharge power setting mapis set in advance to specify a relationship between the state of chargeSOC and the required charge discharge power Pb1* of the battery 50 andis stored in the non-illustrated ROM.

FIG. 11 is a diagram illustrating one example of the required chargedischarge power setting map. As illustrated, when the state of chargeSOC of the battery 50 is equal to the target state of charge SOC*, therequired charge discharge power Pb1* of the battery 50 is set to a value0. Furthermore, when the state of charge SOC is higher than the targetstate of charge SOC*, the required charge discharge power Pb1* is set toincrease from a value 0 to a predetermined discharging (positive) powerPdi1 with an increase in the state of charge SOC and to be kept constantat the predetermined power Pdi1. Moreover, when the state of charge SOCis lower than the target state of charge SOC*, the required chargedischarge power Pb1* is set to decrease from the value 0 to apredetermined charging (negative) power Pch1 with a decrease in thestate of charge SOC and to be kept constant at the predetermined powerPch1.

The HVECU 70 subsequently calculates an upper limit driving force Tdlim1by dividing the sum of the upper limit power Pelim of the engine 22 andthe required charge discharge power Pb1* of the battery 50 by therotation speed Nd of the driveshaft 36 according to Expression (1) givenbelow (step S180). The upper limit driving force Tdlim1 denotes an upperlimit of driving force that can be output to the driveshaft 36 when theupper limit power Pelim is output from the engine 22 that is operated atthe target rotation speed Ne* (drivability rotation speed Nedrv) and thebattery 50 is charged or discharged with the required charge dischargepower Pb1*. In Expression (1), the required charge discharge power Pb1*of the battery 50 is added to the upper limit power Pelim of the engine22, with a view to suppressing a variation in power output from theengine 22 when the battery 50 is charged or discharged with the requiredcharge discharge power Pb1*.

Tdlim1=(Pelim+Pb1*)/Nd  (1)

The HVECU 70 subsequently compares the required driving force Tdusr withthe upper limit driving force Tdlim1 (step S190). Such comparison is aprocess of determining whether or not the required driving force Tdusrcan be output to the driveshaft 36, accompanied with charge or dischargeof the battery 50 with the required charge discharge power Pb1*.

When the required driving force Tdusr is equal to or smaller than theupper limit driving force Tdlim1, the HVECU 70 determines that therequired driving force Tdusr can be output to the driveshaft 36,accompanied with charge or discharge of the battery 50 with the requiredcharge discharge power Pb1*. The HVECU 70 then sets a required chargedischarge power Pb2* as the working compensation power of the battery 50(which has a positive value when the battery 50 is discharged) to avalue 0 (step S200). The HVECU 70 subsequently sets a target drivingforce Td* that is to be output to the driveshaft 36 to the requireddriving force Tdusr (step S210). The details of the required chargedischarge power Pb2* of the battery 50 will be described later.

The HVECU 70 subsequently calculates a target power Pe* that is to beoutput from the engine 22 by subtracting the required charge dischargepower Pb1* of the battery 50 from the product of the target drivingforce Td* and the rotation speed Nd of the driveshaft 36 according toExpression (2) given below (step S220). In Expression (2), the productof the target driving force Td* and the rotation speed Nd of thedriveshaft 36 denotes a target power Pd* that is to be output to thedriveshaft 36. The target power Pe* of the engine 22 obtained byExpression (2) denotes a power of the engine 22 required to output thetarget driving force Td* to the driveshaft 36, accompanied with chargeor discharge of the battery 50 with the required charge discharge powerPb1*. Furthermore, in this state, the required driving force Tdusr isequal to or smaller than the upper limit driving force Tdlim1. By takinginto account Expression (1) and Expression (2), it is understood thatthe target power Pe* of the engine 22 is equal to or smaller than theupper limit power Pelim.

Pe*=Td*·Nd−Pd1*  (2)

After setting the target power Pe* and the target rotation speed Ne* ofthe engine 22, the HVECU 70 calculates a torque command Tm1* of themotor MG1 according to Expression (3) given below by using the rotationspeed Ne, the target rotation speed Ne* and the target power Pe* of theengine 22 and the gear ratio ρ0 of the planetary gear 30 (step S320).Expression (3) is a relational expression of feedback control to rotatethe engine 22 at the target rotation speed Ne*. In Expression (3), afirst term on the right side is a feedforward term, a second term on theright side is a proportional of a feedback term, and a third term on theright side is an integral term of the feedback term. The first term onthe right side indicates a torque that causes the motor MG1 to receive atorque output from the engine 22 and applied to the rotating shaft ofthe motor MG1 via the planetary gear 30. In Expression (3), “kp” of thesecond term on the right side denotes a gain of the proportional, and“ki” of the third term on the right side denotes a gain of the integralterm.

Tm1*=−(Pe*/Ne*)·[ρ0/(1+ρ0)]+kp·(Ne*−Ne)+ki·∫(Ne*−Ne)dt  (3)

The HVECU 70 subsequently calculates a target driving force Tin* that isto be output to the input shaft 61 of the stepped transmission 60 bydividing the target driving force Td* by a gear ratio Grat of thestepped transmission 60 (step S330). The gear ratio Grat of the steppedtransmission 60 used here is, for example, a value obtained by dividingthe rotation speed Nm2 of the motor MG2 (i.e., the rotation speed of theinput shaft 61 of the stepped transmission 60) by the rotation speed Ndof the driveshaft 36.

The HVECU 70 subsequently calculates a tentative torque Tm2tmp that is atentative value of a torque command Tm2* of the motor MG2 by subtractinga torque (−Tm1*/ρ0) from the target driving force Tin* according toExpression (4) given below (step S340). in Expression (4), the torque(−Tm1*/ρ0) denotes a torque output from the motor MG1 and applied to thedriveshaft 36 via the planetary gear 30 when the motor MG1 is drivenwith the torque command Tm1*.

Tm2tmp=Tin*+Tm1*/ρ0  (4)

The HVECU 70 subsequently calculates a torque limit Tm2max of the motorMG1 by subtracting the product of the torque command Tm1* and therotation speed Nm1 of the motor MG2 from the output limit Wout of thebattery 50 and dividing the difference by the rotation speed Nm2 of themotor MG2 according to Expression (5) given below (step S350). InExpression (5), the product of the torque command Tm1* and the rotationspeed Nm1 of the motor MG1 denotes an electric power of the motor MG1(which has a positive value when the motor MG1 is power-driven). TheHVECU 70 then sets the torque command Tm2* of the motor MG2 to thesmaller between the tentative torque Tm2tmp and the torque limit Tm2maxof the motor MG2 according to Expression (6) given below (step S360).

Tm2max=(Wout−Tm1*·Nm1)/Nm2  (5)

Tm2*=min(Tm2tmp,Tm2max)  (6)

After obtaining the target power Pe* and the target rotation speed Ne*of the engine 22 and the torque commands Tm1* and Tm2* of the motors MG1and MG2, the HVECU 70 sends the target power Pe* and the target rotationspeed Ne* of the engine 22 to the engine ECU 24 and sends the torquecommands Tm1* and Tm2* of the motors MG1 and MG2 to the motor ECU 40(step S370) and then terminates this routine.

When receiving the target power Pe* and the target rotation speed Ne* ofthe engine 22, the engine ECU 24 performs operation control of theengine 22 (for example, intake air flow control, fuel injection controland ignition control), such that the engine 22 is operated based on thetarget power Pe* and the target rotation speed Ne*. When receiving thetorque commands Tm1* and Tm2* of the motors MG1 and MG2, the motor ECU40 performs switching control of the plurality of switching elementsincluded in the inverters 41 and 42, such that the motors MG1 and MG2are respectively driven with the torque commands Tm1* and Tm2*.

When the required driving force Tdusr is equal to or smaller than theupper limit driving force Tdlim1, the HVECU 70 in cooperation with theengine ECU 24 and the motor ECU 40 controls the engine 22 and the motorsMG1 and MG2, such that the engine 22 is operated at the target rotationspeed Ne* (drivability rotation speed Nedrv) and that the target drivingforce Td* set to the required driving force Tdusr is output to thedriveshaft 36 in the range of the output limit Wout of the battery 50.

When the required driving force Tdusr is larger than the upper limitdriving force Tdlim1 at step S190, on the other hand, the HVECU 70determines that the required driving force Tdusr cannot be output to thedriveshaft 36, accompanied with charge or discharge of the battery 50with the required charge discharge power Pb1*. In this state, the HVECU70 determines that there is a requirement for battery powercompensation. The battery power compensation aims to make the drivingforce that can be output to the driveshaft 36 larger than the upperlimit driving force Tdlim1 by charging or discharging the battery 50with such an electric power that is larger on the discharge side (thatis smaller on the charge side) than the required charge discharge powerPb1*.

The HVECU 70 subsequently calculates a required compensation powerPcoreq of the battery 50 by subtracting the upper limit driving forceTdlim1 from the required driving force Tdusr and multiplying thedifference by the rotation speed Nd of the driveshaft 36 according toExpression (7) given below (step S230). The HVECU 70 subsequently sets acompensable power Pcolim (i.e., a power allowed to compensate for ashortage) of the battery 50 in a range of not higher than the outputlimit Wout of the battery 50 according to a compensable power settingmap by using the state of charge SOC of the battery 50 (step S240). Thecompensable power setting map is set in advance to specify arelationship between the state of charge SOC and the compensable powerPcolim of the battery 50 and is stored in the non-illustrated ROM.

Pcoreq=(Tdusr−Tdlim1)·Nd  (7)

FIG. 12 is a diagram illustrating one example of the compensable powersetting map. As illustrated, when the state of charge SOC of the battery50 is equal to or higher than a reference value Slo1 that is smallerthan the target state of charge SOC*, the compensable power Pcolim ofthe battery 50 is set to a predetermined discharging power Pdi2 that issufficiently larger than the predetermined power Pdi1 described above.When the state of charge SOC is lower than the reference value Slo1 andis also higher than a reference value Slo2 that is smaller than thereference value Slo1, the compensable power Pcolim is set to decreasefrom the predetermined power Pdi2 to a value 0 with a decrease in thestate of charge SOC. Additionally, when the state of charge SOC is equalto or lower than the reference value Slo2, the compensable power Pcolimis set to the value 0.

After obtaining the required compensation power Pcoreq and thecompensable power Pcolim of the battery 50, the HVECU 70 sets a targetcompensation power Pcotag of the battery 50 to the smaller between therequired compensation power Pcoreq and the compensable power Pcolim ofthe battery 50 according to Expression (8) given below (step S250).

Pcotag=min(Pcoreq,Pcolim)  (8)

The HVECU 70 subsequently determines whether the gear ratio Gsat of thestepped transmission 60 is changed (shifted) (step S260). The gear ratioGsat is changed, for example, after the gear shift Gsat and the targetgear ratio Gsat* are different (after it is determined that the gearposition Gsat is changed) until the inertia phase control starts oruntil the change of the gear ratio Gsat is completed. The battery powercompensation is required and the gear ratio Gsat is not changed, whenthe battery power compensation is required due to a change in thesimulated gear ratio Gsv while keeping the gear ratio Gsat unchanged(for example, a change from the forward gear ratio of the second speedto the third speed), or when the battery power compensation is requiredwhile keeping the simulated gear ratio Gsv and the target gear ratioGsat* unchanged, for example.

When it is determined at step S260 that the gear ratio Gsat of thestepped transmission 60 is not changed, the HVECU 70 sets a rating valueα to a relatively large predetermined value α1 (step S270). When it isdetermined that the gear ratio Gsat of the stepped transmission 60 ischanged, on the other hand, the HVECU 70 sets the rating value α to apredetermined value α2 that is smaller than the predetermined value α1(step S272). The reason of such setting of the rating value α will bedescribed later.

The HVECU 70 subsequently sets the required charge discharge power Pb2*as the working compensation power of the battery 50 to the smallerbetween a value obtained by adding the rating value α to a previousrequired charge discharge power (previous working compensation power:previous Pb2*) and the target compensation power Pcotag of the battery50 according to Expression (9) given below (step S280). Such setting ofstep S280 is a process of calculating the required charge dischargepower Pb2* of the battery 50 by a rating process of the targetcompensation power Pcotag of the battery 50 using the rating value α.

Pb2*=min(Previous Pb2*+a,Pcotag)  (9)

Accordingly, when the requirement for battery power compensation isongoing, the HVECU 70 repeatedly performs this routine, so as togradually increase the required charge discharge power Pb2* of thebattery 50 toward the target compensation power Pcotag of the battery 50by using the rating value α. In the embodiment, as the HVECU 70 uses asmaller rating value α when the gear ratio Gsat of the steppedtransmission 60 is changed compared to when the gear ratio Gsat is notchanged, the HVECU 70 gradually increases the required charge dischargepower Pb2* of the battery 50. After the required charge discharge powerPb2* of the battery 50 reaches the target compensation power Pcotag, theHVECU 70 gradually decreases the required charge discharge power Pb2* ofthe battery 50 (to a value 0) with a gradual decrease in the differencebetween the required driving force Tdusr and the upper limit drivingforce Tdlim1 (to a value 0), i.e., a gradual decrease in the targetcompensation power Pcotag.

After obtaining the required charge discharge power Pb2* of the battery50, the HVECU 70 calculates an upper limit driving force Tdlim2 bydividing a total sum of the upper limit power Pelim of the engine 22 andthe required charge discharge powers Pb1* and Pb2* of the battery 50 bythe rotation speed Nd of the driveshaft 36 according to Expression (10)given below (step S290).

Tdlim2=(Pelim+(Pb1*+Pb2*))/Nd  (10)

The upper limit driving force Tdlim2 denotes an upper limit of drivingforce that can be output to the driveshaft 36 when the upper limit powerPelim is output from the engine 22 that is operated at the targetrotation speed Ne* (drivability rotation speed Nedrv) and the battery 50is charged or discharged with the total power of the required chargedischarge powers Pb1* and Pb2*. This upper limit driving force Tdlim2differs from the upper limit driving force Tdlim1 described above, sincethe upper limit driving force Tdlim2 is determined by taking intoaccount the required charge discharge power Pb2* of the battery 50. InExpression (10), the sum of the required charge discharge powers Pb1*and Pb2* of the battery 50 is added to the upper limit power Pelim ofthe engine 22, with a view to suppressing a variation in power outputfrom the engine 22 when the battery 50 is charged or discharged with thetotal power of the required charge discharge powers Pb1* and Pb2*.

After obtaining the upper limit driving force Tdlim2, the HVECU 70 setsthe target driving force Td* to the smaller between the required drivingforce Tdusr and the upper limit driving force Tdlim2 according toExpression (11) given below (step S300). The HVECU 70 subsequentlycalculates the target power Pe* of the engine 22 by subtracting the sumof the required charge discharge powers Pb1* and Pb2* of the battery 50from the product of the target driving force Td* and the rotation speedNd of the driveshaft 36 according to Expression (12) given below (stepS310), performs the processing of steps S320 to S370 and then terminatesthis routine.

Td*=min(Tdusr,Tdlim2)  (11)

Pe*=Td*·Nd−(Pb1*+Pb2*)  (12)

The target power Pe* of the engine 22 obtained by Expression (12)denotes a power of the engine 22 required to output the target drivingforce Td* to the driveshaft 36, accompanied with charge or discharge ofthe battery 50 with the total power of the required charge dischargepowers Pb1* and Pb2*. The HVECU 70 sets the target driving force Td* tothe smaller between the required driving force Tdusr and the upper limitdriving force Tdlim2. By taking into account Expression (10) andExpression (12) given above, it is accordingly understood that thetarget power Pe* of the engine 22 becomes equal to or smaller than theupper limit power Pelim. Additionally, the processing of steps S290,S300 and S330 to S360 causes the required charge discharge power Pb2* ofthe battery 50 to be reflected on the upper limit driving force Tdlim2,the target driving force Td*, the target driving force Tin* and thetorque command Tm2* of the motor MG2 and thereby to be reflected on thedriving force output to the driveshaft 36.

The HVECU 70 performs the control described above to set the upper limitdriving force Tdlim2, based on the total sum of the upper limit powerPelim of the engine 22 and the required charge discharge powers Pb1* andPb2* of the battery 50, when the required driving force Tdusr is largerthan the upper limit driving force Tdlim1. The HVECU 70 in cooperationwith the engine ECU 24 and the motor ECU 40 controls the engine 22 andthe motors MG1 and MG2, such that the engine 22 is operated at thetarget rotation speed Ne* (drivability rotation speed Nedrv) and thatthe target driving force Td* set to the the smaller between the requireddriving force Tdusr and the upper limit driving force Tdlim2 is outputto the driveshaft 36 in the range of the output limit Wout of thebattery 50. The hybrid vehicle 20 enables a larger driving force thanthe upper limit driving force Tdlim1 to be output to the driveshaft 36by charging or discharging the battery 50 with the total power of therequired charge discharge powers Pb1* and Pb2*. In other words, batterypower compensation is performed in the hybrid vehicle 20. The hybridvehicle 20 accordingly suppresses a reduction of the driving forceoutput to the driveshaft 36 when the upper limit driving force Tdlim1decreases in the course of upshift of the simulated gear ratio Gsv tobecome smaller than the required driving force Tdusr. As a result, thehybrid vehicle 20 suppresses deterioration of the driver's drivefeeling.

Further, in the case where the required driving force Tdusr is largerthan the upper limit driving force Tdlim1, when the gear ratio Gsat ofthe stepped transmission 60 is changed (shifted), the HVECU 70 increasesthe required charge discharge power Pb2* of the battery 50 toward therequired compensation power Pcoreq by using the smaller rating value αcompared to when the gear ratio Gsat is not changed. Accordingly, thehybrid vehicle 20 of the present disclosure further suppresses thevariation of the driving force output to the drive shaft 36 with thechange of the gear ratio Gsat of the stepped transmission 60, andsuppresses the gear shift shock.

FIG. 13 is a diagram illustrating one example of variations in theaccelerator position Acc, the vehicle speed V, the simulated gear ratioGsv, the target gear ratio Gsat*, the target rotation speed Ne* and theactual rotation speed Ne of the engine 22, the target power Pe* and theactual output power Pe of the engine 22, the required driving forceTdusr, the upper limit driving force Tdlim1, the required chargedischarge power Pb1* and Pb2* and the actual charge discharge power Pbof the battery 50, the target driving force Td*, and the actual drivingforce output to the drive shaft 36 (output driving force Td) when thegear ratio Gsat of the stepped transmission 60 is not changed. In thisdiagram, the target compensation power Pcotag of the battery 50 isadditionally shown in the graph of the required charge discharge powerPb2* of the battery 50 for the purpose of reference. In the diagram,solid line curves indicate variations of the embodiment and one-dotchain line curves indicate variations of a comparative example withregard to the required charge discharge power Pb2* and the chargedischarge power Pb of the battery 50, the target driving force Td* andthe output driving force Td. The comparative example is a case where therequired charge discharge power Pb2* of the battery 50 is not taken intoaccount, i.e., a case where the required charge discharge power Pb2* ofthe battery 50 is set to the value 0 irrespective of the magnituderelationship between the required driving force Tdusr and the upperlimit driving force Tdlim1 and where the upper limit driving forcesTdlim1 and Tdlim2 are equal to each other.

As illustrated, the comparative example has a reduction of the outputdriving force Td relative to the required driving force Tdusr for a timeperiod when the required driving force Tdusr is equal to or larger thanthe upper limit driving force Tdlim1 after the upper limit driving forceTdlim1 decreases in the course of upshift of the simulated gear ratioGsv to become smaller than the required driving force Tdusr (for a timeperiod of t11 to t12). The reduction of the output driving force Tdrelative to the required driving force Tdusr differs from the reductionof the target driving force Td* relative to the required driving forceTdusr based on a response delay of the rotation speed Ne and the outputpower Pe relative to the target rotation speed Ne* and the target powerPe* of the engine 22.

In the embodiment, on the other hand, when the upper limit driving forceTdlim1 decreases in the course of upshift of the simulated gear ratioGsv to become smaller than the required driving force Tdusr (at a timet11), the required charge discharge power Pb2* and accordingly thecharge discharge power Pb of the battery 50 increase toward the targetcompensation power Pcotag to reach the target compensation power Pcotag,so that the target driving force Td* and accordingly the output drivingforce Td become larger than the upper limit driving force Tdlim1 (for atime period of t11 to t12). The hybrid vehicle 20 of this configurationaccordingly suppresses a reduction of the output driving force Tdrelative to the required driving force Tdusr.

FIG. 14 is a diagram illustrating one example of variations in theaccelerator position Acc, the vehicle speed V, the simulated gear ratioGsv, the target gear ratio Gsat*, the required driving force Tdusr, therequired charge discharge power Pb2* of the battery 50, and a torquecommand Tm2* of the motor MG2 when the gear ratio Gsat of the steppedtransmission 60 is upshifted. In the diagram, solid line curves indicatevariations of the embodiment and one-dot chain line curves indicatevariations of a comparative example with regard to the required chargedischarge power Pb2* of the battery 50 and the torque command Tm2* ofthe motor MG2. As the comparative example, the rating value α is set tothe predetermined value α1 even when the gear ratio Gsat of the steppedtransmission 60 is changed, which is the same as when the gear stageGsat is not changed.

As illustrated, in the comparative example, when the requirement for thebattery power compensation is started accompanied with the upshift ofthe simulated gear ratio Gsv and the target gear ratio Gsat* (at a timet21), the rating value α is set to the relatively large predeterminedvalue α1, and the required charge discharge power Pb2* of the battery 50is increased toward the target compensation power Pcotag by using theset rating value α. Accordingly, the increase of the required chargedischarge power Pb2* of the battery 50 and accordingly the increase ofthe torque command Tm2* of the motor MG2 (increase of the torque outputto the input shaft 61 of the stepped transmission 60 from the motor MG2)becomes relatively abrupt. The variation of the output driving force Tdthat is output to the drive shaft 36 may occur with the change of thegear ratio Gsat of the stepped transmission 60, and the gear shift shockmay be caused.

In the embodiment, on the other hand, when the requirement for thebattery power compensation is started accompanied with the upshift ofthe simulated gear ratio Gsv and the target gear ratio Gsat* (at a timet21), the rating value α is set to the predetermined value α2, that issmaller than the predetermined value α1, and the required chargedischarge power Pb2* of the battery 50 is increased toward the targetcompensation power Pcotag by using the set rating value α. Accordingly,compared to the comparative example, the increase of the required chargedischarge power Pb2* of the battery 50 and accordingly the increase ofthe torque command Tm2* of the motor MG2 (increase of the torque outputto the input shaft 61 of the stepped transmission 60 from the motor MG2)becomes gradual. As a result, the hybrid vehicle 20 of the presentdisclosure suppresses the variation of the driving force output to thedrive shaft 36 with the change of the gear ratio Gsat of the steppedtransmission 60, and suppresses the gear shift shock.

In the hybrid vehicle 20 of the embodiment described above, in the casewhere the required driving force Tdusr becomes larger than the upperlimit driving force Tdlim1 and the battery power compensation isrequired, the HVECU 70 increases the required charge discharge powerPb2* of the battery 50 toward the target compensation power Pcotag byusing the smaller rating value α when the gear ratio Gsat of the steppedtransmission 60 is changed, compared to when the gear ratio Gsat is notchanged. As a result, the hybrid vehicle 20 of the present disclosuresuppresses the variation of the driving force output to the drive shaft36 with the change of the gear ratio Gsat of the stepped transmission60, and suppresses the gear shift shock.

In the hybrid vehicle 20 of the embodiment, the HVECU 70 performs thedrivability priority control routine of FIG. 5 and FIG. 6. The HVECU 70may, however, perform the drivability priority control routine (firsthalf) of FIG. 5 and the drivability priority control routine (latterhalf) of FIG. 15. The drivability priority control routine of FIG. 15 issimilar to the drivability priority control routine of FIG. 6, exceptaddition of the processing of step S400 to S420. The description of theprocessing of the steps S200 to S220 and S320 to S370 of the drivabilitypriority control routine of FIG. 15 are accordingly omitted.

After setting of the target compensation power Pcotag of the battery 50at step S250 and before the processing of step S260 of the drivabilitypriority control routine of FIG. 5, in the drivability priority controlroutine of FIG. 15, the HVECU 70 compares the accelerator position Accwith the reference value Aref (step S400) and compares the vehicle speedV with the reference value Vref (step S410). The reference value Aref isa reference value used to determine whether the driver is requesting arapid acceleration. The reference value Vref is a reference value usedto determine whether the vehicle is driven in a high speed.

In this state, the required driving force Tdusr is larger than the upperlimit driving force Tdlim1 at step S190, that is, the battery powercompensation is required. The battery power compensation is a processingin which the charge discharge power Pb of the battery 50 is increased tothe discharge side (reduced to the charge side) so that the drivingforce that is larger than the upper limit driving force Tdlim1 can beoutput to the drive shaft 36 while maintaining quietness. It isconsidered that there is no need to perform the battery powercompensation when the driver is requesting a rapid acceleration or thevehicle is driven in a high speed (the vehicle is driven with big roadnoise). The steps S400 and S401 are the process of determining whetherthe battery power compensation is needed.

When the accelerator position Acc is equal to or smaller than thereference value Aref at step S400 and the vehicle speed V is equal to orlower than the reference value Vref at step S410, the HVECU 70determines that the battery power compensation is needed and performsthe processing of and after step S260.

When the accelerator position Acc is larger than the reference valueAref at step S400 and the vehicle speed V is higher than the referencevalue Vref at step S410, the HVECU 70 determines that the battery powercompensation is not needed, sets the required charge discharge powerPb2* of the battery 50 to the larger between the value determined bysubtracting a rating value β from the previous working compensationpower (previous Pb2*) of the battery 50 and the value 0 according toExpression (13) given below (step S420), and performs the processing ofand after step S290. The rating value β is set in advance as a value todecrease the required charge discharge power Pb2* of the battery 50 tothe value 0 abruptly (in a short time). The step S420 is a process todecrease the required charge discharge power Pb2* of the battery 50 tothe value 0 to keep the required charge discharge power Pb2* at thevalue 0 by performing the rating process using the rating value β.

Pb2*=max(Previous Pb2*−β,0)  (13)

The HVECU 70 performs the control described above to decrease therequired charge discharge power Pb2* of the battery 50 to the value 0abruptly and terminate the battery power compensation when theaccelerator position Acc becomes larger than the reference value Arefand the vehicle speed V becomes higher than the reference value Vrefwhen the required charge discharge power Pb2* of the battery 50 has apositive value (performing the battery power compensation). Thissuppresses wasteful battery power compensation and also suppresses thedecrease of state of charge SOC of the battery 50.

FIG. 16 is a diagram illustrating one example of variations in theaccelerator position Acc, the vehicle speed V, the simulated gear ratioGsv, the target gear ratio Gsat*, the required driving force Tdusr, therequired charge discharge power Pb2* of the battery 50, and the torquecommand Tm2* of the motor MG2 when the accelerator position Acc becomeslarger than the reference value Aref during the battery powercompensation. In the diagram, solid line curves indicate variations ofthis modification (performing the drivability priority control routineof FIG. 5 and FIG. 15) and one-dot chain line curves indicate variationsof the embodiment (performing the drivability priority control routineof FIG. 5 and FIG. 6) with regard to the required charge discharge powerPb2* of the battery 50 and the torque command Tm2* of the motor MG2.

As illustrated, in the modification, when the requirement for thebattery power compensation is started accompanied with the upshift ofthe simulated gear ratio Gsv (at a time t31), the required chargedischarge power Pb2* of the battery 50 is increased from the value 0.When the accelerator position Acc becomes larger than the referencevalue Aref when the required charge discharge power Pb2* of the battery50 has a positive value (at a time t32), the required charge dischargepower Pb2* of the battery 50 is decreased abruptly. This suppresseswasteful battery power compensation and also suppresses the decrease ofstate of charge SOC of the battery 50 compared with the embodiment.

In the modification, the HVECU 70 performs the drivability prioritycontrol routine (first half) of FIG. 5 and the drivability prioritycontrol routine (latter half) of FIG. 15. The HVECU 70 may, however,perform the drivability priority control routine (first half) of FIG. 5and the drivability priority control routine (latter half) of FIG. 17.The drivability priority control routine of FIG. 17 is similar to thedrivability priority control routine of FIG. 15, except addition of theprocessing of steps S500 and S510.

In the drivability priority control routine of FIG. 17, when theaccelerator position Acc is larger than the reference value Aref at stepS400 or when the vehicle speed V is higher than the reference value Vrefat step S410, the HVECU 70 determines, like the processing of step S260,whether the gear ratio Gsat of the stepped transmission 60 is changed(shifted) (step S500). When the gear ratio Gsat of the steppedtransmission 60 is not changed, the HVECU 70 performs the processing ofand after step S420.

When the gear ratio Gsat of the stepped transmission 60 is changed atstep S500, the HVECU 70 sets a required charge discharge power Pb2* tothe previous required charge discharge power (previous Pb2*) of thebattery 50, that is, the HVECU 70 keeps the required charge dischargepower Pb2* of the battery 50 (step S510), and performs the processing ofand after step S290.

According to the control described above, when the accelerator positionAcc is larger than the reference value Aref or when the vehicle speed Vis higher than the reference value Vref while the battery powercompensation is required, and when the gear ratio Gsat of the powertransmission 60 is changed, the required charge discharge power Pb2* ofthe battery 50 is kept unchanged. This suppresses the required chargedischarge power Pb2* and accordingly the torque command Tm2* of themotor MG2 (a torque output to the input shaft 61 of the steppedtransmission 60 from the motor MG2) to be changed and also suppressesthe driving force output to the drive shaft 36 to be changed when thegear ratio Gsat of the stepped transmission 60 is changed.

FIG. 18 is a diagram illustrating one example of variations in theaccelerator position Acc, the vehicle speed V, the simulated gear ratioGsv, the target gear ratio Gsat*, the required driving force Tdusr, therequired charge discharge power Pb2* of the battery 50, and the torquecommand Tm2* of the motor MG2 when the accelerator position Acc becomeslarger than the reference value Aref during a battery powercompensation, and subsequently, the charge discharge power Pb* of thebattery 50 has a positive value and the gear ratio Gsat of the steppedtransmission 60 is changed. In the diagram, solid line curves indicatevariations of this modification (performing the drivability prioritycontrol routine of FIG. 5 and FIG. 15) and one-dot chain line curvesindicate variations of the embodiment (performing the drivabilitypriority control routine of FIG. 5 and FIG. 6) with regard to therequired charge discharge power Pb2* of the battery 50 and the torquecommand Tm2* of the motor MG2.

As illustrated, in the modification, when the requirement for thebattery power compensation is started accompanied with the upshift ofthe simulated gear ratio Gsv (at a time t41), the required chargedischarge power Pb2* of the battery 50 is increased from the value 0.When the accelerator position Acc becomes larger than the referencevalue Aref when the required charge discharge power Pb2* of the battery50 has a positive value (at a time t42), the required charge dischargepower Pb2* of the battery 50 is decreased abruptly. When the requiredcharge discharge power Pb2* of the battery 50 has a positive value, thetarget gear ratio Gsat* is upshifted, and the gear ratio Gsat isupshifted (for a time period of t43 to t44), the required chargedischarge power Pb2* of the battery 50 is kept unchanged. Thissuppresses the required charge discharge power Pb2* and accordingly thetorque command Tm2* of the motor MG2 (a torque output to the input shaft61 of the stepped transmission 60 from the motor MG2) to be changed andalso suppresses the driving force output to the drive shaft 36 to bechanged when the gear ratio Gsat of the stepped transmission 60 ischanged.

In the hybrid vehicle 20 of the embodiment, the HVECU 70 performs thedrivability priority control routine of FIG. 5 and FIG. 6. The HVECU 70may, however, perform the drivability priority control routine (firsthalf) of FIG. 5 and the drivability priority control routine (latterhalf) of FIG. 19. The drivability priority control routine of FIG. 19 issimilar to the drivability priority control routine of FIG. 6, exceptaddition of the processing of step S600 to S630. The description of theprocessing of the step S200 to S220 and S320 to S370 of the drivabilitypriority control routine of FIG. 19 is accordingly omitted.

After setting of the target compensation power Pcotag of the battery 50at step S250 and before the processing of step S260 of the drivabilitypriority control routine of FIG. 5, in the drivability priority controlroutine of FIG. 19, the HVECU 70 compares the previous required drivingforce (previous Tdusr) with the previous first upper limit driving force(previous Tdlim1) (step S600). Such comparison is a process ofdetermining whether it is a timing immediately after the requireddriving force Tdusr becomes larger than the upper limit driving forceTdlim1, i.e., whether it is a timing immediately after a start of therequirement for battery power compensation.

When the previous required driving force (previous Tdusr) is equal to orsmaller than the previous first upper limit driving force (previousTdlim1) at step S600, the HVECU 70 determines that it is the timingimmediately after the start of the requirement for battery powercompensation and performs the processing of and after step S260.

When the previous required driving force (previous Tdusr) is larger thanthe previous first upper limit driving force (previous Tdlim1) at stepS600, the HVECU 70 determines that it is not the timing immediatelyafter the start of the requirement for battery power compensation (thisrequirement is being continued), and compares the previous requiredcharge discharge power (previous Pb2*) with the required chargedischarge power before the last (before last Pb2*) (step S610). Suchcomparison is a process of determining whether the required chargedischarge power Pb2* of the battery 50 is decreasing with a decrease ofthe target compensation power Pcotag after the required charge dischargepower Pb2* of the battery 50 reached the target compensation powerPcotag.

When the previous required charge discharge power (previous Pb2*) isequal to or larger than the required charge discharge power before thelast (before last Pb2*) at step S610, the HVECU 70 determines that therequired charge discharge power Pb2* of the battery 50 is not decreasingand performs the processing of and after step S280.

When the previous required charge discharge power of the battery 50(previous Pb2*) is smaller than the required charge discharge powerbefore the last (before last Pb2*) at step S610, the HVECU 70 determinesthat the required charge discharge power Pb2* of the battery 50 isdecreasing. The HVECU 70 further determines, like the processing of stepS260, whether the gear ratio Gsat of the stepped transmission 60 ischanged (shifted) (step S620). When the gear ratio Gsat of the steppedtransmission 60 is not changed, the HVECU 70 performs the processing ofand after step S280.

When the gear ratio Gsat of the stepped transmission 60 is changed(shifted) at step S620, the HVECU 70 sets a required charge dischargepower Pb2* to the previous required charge discharge power (previousPb2*) of the battery 50, that is, the required charge discharge powerPb2* of the battery 50 is kept unchanged (step S630), and performs theprocessing of and after step S290. This suppresses the required chargedischarge power Pb2* and accordingly the torque command Tm2* of themotor MG2 (a torque output to the input shaft 61 of the steppedtransmission 60 from the motor MG2) to be changed and also suppressesthe driving force output to the drive shaft 36 to be changed when thegear ratio Gsat of the stepped transmission 60 is changed.

In the hybrid vehicle 20 of the embodiment, the HVECU 70 processes thetarget compensation power Pcotag of the battery 50 by the rating processusing the rating value α to calculate the required charge dischargepower Pb2* of the battery 50. According to a modification, the HVECU 70may process the target compensation power Pcotag of the battery 50 by asmoothing process using a time constant τ to calculate the requiredcharge discharge power Pb2* of the battery 50. In this case, when thegear ratio Gsat of the stepped transmission 60 is not changed, the HVECU70 may set a relatively small predetermined value τ1 to the timeconstant T. When the gear ratio Gsat of the stepped transmission 60 ischanged, the HVECU 70 may set a predetermined value τ2 that is largerthan the predetermined value τ1 to the time constant T.

The hybrid vehicle 20 of the embodiment is provided with the mode switch90. The HVECU 70 performs the drivability priority control routine ofFIGS. 5 and 6 when the hybrid vehicle 20 is driven by HV drive at theshift position SP set to the D position with selection of thedrivability priority mode as the working drive mode by the driver'soperation of the mode switch 90. According to a modification, the hybridvehicle 20 may not be provided with the mode switch 90. The HVECU 70 mayperform the drivability priority control routine of FIGS. 5 and 6 whenthe hybrid vehicle 20 is driven by HV drive at the shift position SP setto the D position in the ordinary mode.

The hybrid vehicle 20 of the embodiment has the parking position (Pposition), the reverse position (R position), the neutral position (Nposition) and the drive position (D position) provided as the shiftposition SP. The shift position SP may further include a manual position(M position), in addition to these positions. The manual position (Mposition) is provided with an upshift position (+ position) and adownshift position (− position). When the shift position SP is set tothe manual position (M position), the engine 22 is driven and controlledsuch as to be connected with the driveshaft 36 via the ten-speedsimulated transmission.

The following describes a series of operations when the shift positionSP is set to the manual position (M position). In this case, the HVECU70 may perform a drivability priority control routine (first half) ofFIG. 20 and the drivability priority control routine (latter half) ofFIG. 6, in place of the drivability priority control routines of FIGS. 5and 6. The drivability priority control routine of FIG. 20 is similar tothe drivability priority control routine of FIG. 5, except replacementof the processing of step S100 by the processing of S102 and omission ofthe processing of step S120. The following briefly describes drivecontrol at the shift position SP set to the manual position (M position)with reference to the drivability priority control routine of FIG. 20.

In the drivability priority control routine of FIG. 20, the HVECU 70first obtains input data of, for example, the simulated gear ratio Gsvand the target gear ratio Gsat*, in addition to the accelerator positionAcc, the vehicle speed V, the rotation speed Nd of the driveshaft 36,the rotation speed Ne of the engine 22, the rotation speeds Nm1 and Nm2of the motors MG1 and MG2 and the state of charge SOC and the outputlimit Wout of the battery 50 (step S102). The simulated gear ratio Gsvand the target gear ratio Gsat* input here are values detected based onthe shift position SP.

After obtaining the input data, the HVECU 70 sets the required drivingforce Tdusr according to the required driving force setting map by usingthe accelerator position Acc and the vehicle speed V (step S110). TheHVECU 70 subsequently controls the stepped transmission 60 by using thetarget gear ratio Gsat* (step S130) and performs the processing of andafter step S140. As a result, the same effect as that of the embodimentcan be obtained.

In the hybrid vehicle 20 of the embodiment, the ten-speed simulatedtransmission is configured such that two virtual gear ratios areprovided with regard to each of the gear ratios of the first to thethird speeds of the four-speed stepped transmission 60. The number ofspeeds of the stepped transmission 60 is, however, not limited to thefour speeds but may be two speeds or three speeds or may be five or morespeeds. According to a modification, a desired number of virtual gearratios, for example, one gear ratio or two gear ratios may be providedwith regard to at least one of the gear ratios of the respective speedsof the stepped transmission 60. In this modification, a differentdesired number of gear ratios may be provided with regard to each of thegear ratios of the respective speeds of the stepped transmission 60. Ahybrid vehicle of another modification may not be provided with anyvirtual gear ratios.

In the hybrid vehicle 20 of the embodiment, the motor MG2 is directlyconnected with the input shaft 61 of the stepped transmission 60.According to a modification, the motor MG2 may be connected with theinput shaft 61 of the stepped transmission 60 via a speed reducer or thelike. According to another modification, the motor MG2 may be directlyconnected with the output shaft 62 of the stepped transmission 60.According to another modification, the motor MG2 may be connected withthe output shaft 62 of the stepped transmission 60 via a speed reduceror the like.

The hybrid vehicle 20 of the embodiment uses the battery 50 as the powerstorage device. According to a modification, a capacitor may be used asthe power storage device.

The hybrid vehicle 20 of the embodiment is provided with the engine ECU24, the motor ECU 40, the battery ECU 52 and the HVECU 70. At least twoof these ECUs may be configured as a single electronic control unit.

In the hybrid vehicle of the present disclosure, the control device maybe programmed to reduce the working compensation power, in a case wherethe working compensation power has a positive value and where theoperation amount of the accelerator becomes larger than a predeterminedoperation amount or the vehicle speed becomes higher than apredetermined vehicle speed.

In this case, the control device may be programmed to maintain theworking compensation power, when the gear ratio of the steppedtransmission is changed during reduction of the working compensationpower in the case where the working compensation power has the positivevalue and where the operation amount of the accelerator becomes largerthan the predetermined operation amount or the vehicle speed becomeshigher than the predetermined vehicle speed. This hybrid vehicle cansuppress the change of the working compensation power when the gearratio of the stepped transmission is changed, and can suppress thechange of the driving force of the drive shaft.

In the hybrid vehicle of the present disclosure, the control device maybe programmed to maintain the working compensation power, when the gearratio of the stepped transmission is changed during reduction of theworking compensation power accompanied with a decrease in the targetcompensation power. This hybrid vehicle can suppress the change of theworking compensation power when the gear ratio of the steppedtransmission is changed, and can suppress the change of the drivingforce of the drive shaft.

In the hybrid vehicle of the present disclosure, when setting the firstupper limit driving force, the control device may be programmed to setthe first upper limit driving force to a driving force when a totalpower of the upper limit power and a first required charge dischargepower of the power storage device, which is based on a state of chargeof the power storage device and has a positive value on a dischargeside, is output to the driveshaft, and when setting the second upperlimit driving force, the control device may be programmed to set thesecond upper limit driving force to a driving force when a total powerof the upper limit power, the first required charge discharge power, anda second required charge discharge power of the power storage device,which has a positive value on the discharge side and serves as theworking compensation power, is output to the driveshaft.

In this case, when the required driving force is equal to or smallerthan the first upper limit driving force, the control device may beprogrammed to set a target power of the engine to a power determined bysubtracting the first required charge discharge power from a power thatcauses the target driving force to be output to the driveshaft, and whenthe required driving force is larger than the first upper limit drivingforce, the control device may be programmed to set the target power ofthe engine to a power determined by subtracting a sum of the firstrequired charge discharge power and the second required charge dischargepower from the power that causes the target driving force to be outputto the driveshaft. The control device may be programmed to control theengine such that the target power is output from the engine.

The following describes the correspondence relationship between theprimary elements of the above embodiment and the primary elements of thedisclosure described in Summary. In the embodiment, the engine 22corresponds to the “engine”, the motor MG1 corresponds to the “firstmotor”, the planetary gear 30 corresponds to the “planetary gear”, andthe motor MG2 corresponds to the “second motor”, the battery 50corresponds to the “power storage device” the engine ECU 24, the motorECU 40 and the HVECU 70 correspond to the “control device”.

The correspondence relationship between the primary components of theembodiment and the primary components of the disclosure, regarding whichthe problem is described in Summary, should not be considered to limitthe components of the disclosure, regarding which the problem isdescribed in Summary, since the embodiment is only illustrative tospecifically describes the aspects of the disclosure, regarding whichthe problem is described in Summary. In other words, the disclosure,regarding which the problem is described in Summary, should beinterpreted on the basis of the description in the Summary, and theembodiment is only a specific example of the disclosure, regarding whichthe problem is described in Summary.

The aspect of the disclosure is described above with reference to theembodiment. The disclosure is, however, not limited to the aboveembodiment but various modifications and variations may be made to theembodiment without departing from the scope of the disclosure.

INDUSTRIAL APPLICABILITY

The technique of the disclosure is applicable to the manufacturingindustries of the hybrid vehicle and so on.

What is claimed is:
 1. A hybrid vehicle, comprising an engine; a firstmotor; a planetary gear including three rotational elements that arerespectively connected with the engine, the first motor and atransmission member; a stepped transmission placed between thetransmission member and a driveshaft linked with an axle; a second motorconfigured to input and output power from and to the transmission memberor the driveshaft; a power storage device configured to transmitelectric power to and from the first motor and the second motor; and acontrol device, wherein the control device is programmed to: set arequired driving force that is required for the driveshaft, based on anoperation amount of an accelerator and a vehicle speed; set a simulatedgear ratio from a gear ratio of the stepped transmission or from thegear ratio of the stepped transmission by taking into account a virtualgear ratio and set a target gear ratio of the stepped transmission,based on the operation amount of the accelerator and the vehicle speedor based on a driver's shift operation; set a target rotation speed ofthe engine, based on the vehicle speed and the simulated gear ratio; setan upper limit power of the engine when the engine is operated at thetarget rotation speed; set a first upper limit driving force of thedriveshaft when the upper limit power is output from the engine; set atarget driving force of the driveshaft according to a magnituderelationship between the required driving force and the first upperlimit driving force; and control the engine, the first motor, the secondmotor and the stepped transmission, such that the engine is operated atthe target rotation speed, the gear ratio of the stepped transmissionbecomes equal to the target gear ratio, and the hybrid vehicle is drivenbased on the target driving force, and wherein when the required drivingforce is equal to or smaller than the first upper limit driving force,the control device is programmed to set the target driving force to therequired driving force, and when the required driving force is largerthan the first upper limit driving force, the control device isprogrammed to set a target compensation power of the power storagedevice, based on a difference between the required driving force and thefirst upper limit driving force, the control device is programmed to seta second upper limit driving force of the driveshaft when the upperlimit power is output from the engine and the power storage device ischarged or discharged according to a working compensation power based onthe target compensation power, and the control device is programmed toset the target driving force to the smaller between the required drivingforce and the second upper limit driving force, and wherein the controldevice is programmed to gradually increase the working compensationpower toward the target compensation power when the gear ratio of thestepped transmission is changed, compared with an increase in theworking compensation power when the gear ratio of the steppedtransmission is not changed.
 2. The hybrid vehicle according to claim 1,wherein the control device is programmed to reduce the workingcompensation power, in a case where the working compensation power has apositive value and where the operation amount of the accelerator becomeslarger than a predetermined operation amount or the vehicle speedbecomes higher than a predetermined vehicle speed.
 3. The hybrid vehicleaccording to claim 2, wherein the control device is programmed tomaintain the working compensation power, when the gear ratio of thestepped transmission is changed during reduction of the workingcompensation power in the case where the working compensation power hasthe positive value and where the operation amount of the acceleratorbecomes larger than the predetermined operation amount or the vehiclespeed becomes higher than the predetermined vehicle speed.
 4. The hybridvehicle according to claim 1, wherein the control device is programmedto maintain the working compensation power, when the gear ratio of thestepped transmission is changed during reduction of the workingcompensation power accompanied with a decrease in the targetcompensation power.
 5. The hybrid vehicle according to claim 1, whereinwhen setting the first upper limit driving force, the control device isprogrammed to set the first upper limit driving force to a driving forcewhen a total power of the upper limit power and a first required chargedischarge power of the power storage device, which is based on a stateof charge of the power storage device and has a positive value on adischarge side, is output to the driveshaft, and when setting the secondupper limit driving force, the control device is programmed to set thesecond upper limit driving force to a driving force when a total powerof the upper limit power, the first required charge discharge power, anda second required charge discharge power of the power storage device,which has a positive value on the discharge side and serves as theworking compensation power, is output to the driveshaft.
 6. The hybridvehicle according to claim 5, wherein when the required driving force isequal to or smaller than the first upper limit driving force, thecontrol device is programmed to set a target power of the engine to apower determined by subtracting the first required charge dischargepower from a power that causes the target driving force to be output tothe driveshaft, and when the required driving force is larger than thefirst upper limit driving force, the control device is programmed to setthe target power of the engine to a power determined by subtracting asum of the first required charge discharge power and the second requiredcharge discharge power from the power that causes the target drivingforce to be output to the driveshaft, and wherein the control device isprogrammed to control the engine such that the target power is outputfrom the engine.